Injured or damaged parts of the hard and/or soft tissue of the human body are restored the best by using autologous hard and/or soft tissue. This is not always possible for various reasons, which is why in many cases synthetic material is used as a temporary (biodegradable or post-operatively removable, respectively) or permanent replacement material.
Implants which are anchored in hard and/or soft tissue, serve the temporary or permanent replacement or the support of parts of the musculoskeletal system which have been damaged by accident, use, deficiency or disease, or which have been otherwise degenerated, including especially parts of the chewing apparatus. An implant normally is defined as a synthetic chemically stable material, which is introduced into the body as a plastic replacement or for mechanical enforcement (see e.g. Roche Lexikon Medizin, Urban & Fischer (Publs.); 5th edition 2003). The support- and replacement function in the body is taken over on the basis of the mechanical features and the implant design. Hence, for instance hip- and knee joint prostheses, spine implants and dental implants have been clinically used successfully for many years.
For the anchoring of the implant and the compatibility of the implant at the interface between the implant surface/neighboring tissue, the implant surface has a great significance. Hence, measurements have shown that implants with a smooth surface are anchored, almost independently of the basic material used, only a little in the bone (poor osteointegration), while implants with a structured surface enter into a good mechanical and, at a corresponding design of the surface, also a good biological connection with the surrounding hard- or soft tissue (see Titanium in Medicine, Material Science, Surface Science, Engineering, Biological Responses and Medical Applications Series: Engineering Materials, Brunette, D. M.; Tengvall, P.; Textor, M.; Thomsen, P. (Eds.)).
The time necessary for a sufficient incorporation, an important and central feature for implants, is termed osteointegration time, or, in the dental implant field also osseointegration time, respectively. Thereby, the time is described, which passes by until the bone substance has connected with sufficient force and durably with the implant surface, so to speak, until it has virtually integrated into the implant surface.
Various methods are used for surface treatment, see e.g. in A Guide to Metal and Plastic Finishing (Maroney, Marion L.; 1991); Handbook of Semiconductor Electrodeposition (Applied Physics, 5) (Pandey, R. K., et al.; 1996); Surface Finishing Systems: Metal and Non-Metal Finishing Handbook-Guide (Rudzki, George J.; 1984); Titanium in Medicine, Material Science, Surface Science, Engineering, Biological Responses and Medical Applications Series: Engineering Materials, (Brunette, D. M.; Tengvall, P.; Textor, M.; Thomsen, P. (Eds.)); and Materials and Processes for Surface and Interface Engineering (NATO Asi Series. Series E, Applied Sciences, 115, Pauleau, Ives (Editor); 1995); and the references cited therein.
Besides the surface topology the osseointegration of the implant can be influenced by chemical coatings or modifications of the surface. Thereby, implants can be coated in an aqueous solution containing calcium- and phosphate ions. The resulting surface consists of the two calcium phosphate phases hydroxylapatite and bruschite. This coating is post-operatively replaced by young bone directly on the implant surface within 6-10 weeks and results in a very good healing incorporation of the implants (Zeggel P, Bioactive Calcium Phosphate Coatings for Dental Implants, International Magazine Of Oral Implantology, 1/2000).
The direct modification of an optimized rough surface with fluoride on titanium implants is described as advantageous for the bone healing process by Ellingsen (Ellingsen, J. E. et al., Improved Retention and Bone to Implant Contact with Fluoride Modified Titanium Implants Int. J. Oral Maxillofac Implants (2004); Vol. 19, p. 659-666).
A chemically active, hydrophilic implant surface on titanium implants can be produced by a very elaborate conservation process in a nitrogen atmosphere. The storage of the surface in a solution of sodium chloride conserves the hydrophilic features. Such a surface shall speed up the process of osseointegration and lead to a higher implant stability in the early phase of osseointegration (Ferguson S. J. et al, Biomechanical evaluation of the interfacial strength of a chemically modified sandblasted and acid-etched titanium surface, Journal of Biomedical Materials Research Part A Volume 78A, Issue 2, pages 291-297). Animal studies of the hydrophilic surface show a significantly higher bone-implant contact compared to a hydrophobic surface at the same surface topography (Buser D. et al, Enhanced Bone Apposition to a Chemically Modified SLA Titanium Surface, J. Dent. Res. 83 (7) 529-533 (2004).). These described hydrophilic features can only be produced in a technologically elaborate way and conserved by a special way of storage, during prolonged contact with air the surface assumes a hydrophobic state. Furthermore, the high costs for production and packaging and the limited storage time in a saline solution are problematic for this technology.
From JP 2000-060958, a method is known, in which an implant is firstly, in a first step, treated with a highly concentrated sodium hydroxide solution with a concentration of 5 mole/l, and then sintered under the influence of heat, and in a second step is treated with a calcium hydroxide solution with a concentration in the range of 0.1-20 mole/l during a time span of 10 min to three days at an increased temperature of more than 50° C., followed by explicit washing. Thereby, presumably apatite is produced on the surface, which is supposed to show advantageous effects for the incorporation of the implant.